Your conjecture is convoluted and ambivalent. At least you finally agree there's a parasite within the Baton Pass archetype that's affecting the metagame. That problem is primarily named Scolipede.One thing I'd like to add: if we end up nerfing bp, it should be something definite and permanent. Whatever we decide for bp should last. So I don't think banning specific pokemon or abilities is a good idea, bacause bp can get boosted again by the introduction of new pokemon, abilities or moves in the next gen, which would create the need for this debate all over again. For example, we ban scolipede and then gen 7 introduces a new pokemon with speed boost who is as good as scolipede. No, if bp is gonna be nerfed, it better be nerfed for good, in a way it cannot go back naturally in future gens. Because frankly, I doubt anyone here wants to have this thread again in the future.
So I believe the most fair nerf would be to limit the number of bp pokemon. Since I'm against removing bp teams from the game, I feel like a number like 4 would be ideal, though that's mostly a guess. With a lower number of pokemon with bp,it doesn't matter if bp gets new tools,since it would still me limited by the pokemon cap so it'd have to choose between those tools.
Then again, I'd rather let bp teams remain untouched, but I've already repeated my points on that to exhaustion in the last few days,so I wont do it again.
Then we ban the imaginary 7th Gen Speed Booster if it fills Scolipede's role in an even more optimal way.
Limiting the number of Passers in a team is not only unnecessarily complex, but suboptimal. It does in fact matter if Baton Pass gets new tools: we address them as they come. If some Pokemon releases that fills Scolipede's exact role but better, it'll be unbalanced and detrimental to the development of the metagame with 3 Passers, 4, or 6.